I feel fairly certain that that was perhaps the second or third permutation that I tried; possibly not, however.
In the meantime, I can report I successfully have Discourse v1.7.0.beta10 +42 running on Docker 1.12 on Ubuntu 16.0.4 on a Scaleway VC1S server in Amsterdam, at €2.99/month. For my needs (~10 users), this is perfect. 